Welding Processes A Brief History of Welding Late

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Welding Processes

Welding Processes

A Brief History of Welding • Late 19 th Century • Scientists/engineers apply advances

A Brief History of Welding • Late 19 th Century • Scientists/engineers apply advances in electricity to heat and/or join metals (Le Chatelier, Joule, etc. ) • Early 20 th Century • Prior to WWI welding was not trusted as a method to join two metals due to crack issues • 1930’s and 40’s • Industrial welding gains acceptance and is used extensively in the war effort to build tanks, aircraft, ships, etc. • Modern Welding • the nuclear/space age helps bring welding from an art to a science

Types of Welding Fusion Welding Homogeneous Gas Welding Electroslag High Energy Beam Electric Arc

Types of Welding Fusion Welding Homogeneous Gas Welding Electroslag High Energy Beam Electric Arc Pressure Welding Heterogeneous Brazing Friction Welding Soldering MIG TIG Shielded Metal Arc – “Stick”

Weldability of a Metal • Metallurgical Capacity • Parent metal will join with the

Weldability of a Metal • Metallurgical Capacity • Parent metal will join with the weld metal without formation of deleterious constituents or alloys • Mechanical Soundness • Joint will be free from discontinuities, gas porosity, shrinkage, slag, or cracks • Serviceability • Weld is able to perform under varying conditions or service (e. g. , extreme temperatures, corrosive environments, fatigue, high pressures, etc. )

Fusion Welding Principles • Base metal is melted • Filler metal may be added

Fusion Welding Principles • Base metal is melted • Filler metal may be added • Heat is supplied by various means • • Oxyacetylene gas Electric Arc Plasma Arc Laser

Fusion Welding ELECTRODE COATING CORE WIRE WELDING ATMOSPHERE ARC STREAM ARC POOL SOLIDIFIED SLAG

Fusion Welding ELECTRODE COATING CORE WIRE WELDING ATMOSPHERE ARC STREAM ARC POOL SOLIDIFIED SLAG PENETRATION DEPTH WELD BASE METAL

Weld Metal Protection • During fusion welding, the molten metal in the weld “puddle”

Weld Metal Protection • During fusion welding, the molten metal in the weld “puddle” is susceptible to oxidation • Must protect weld puddle (arc pool) from the atmosphere • Methods • Weld Fluxes • Inert Gases • Vacuum

Weld Fluxes • Typical fluxes • Si. O 2, Ti. O 2, Fe. O,

Weld Fluxes • Typical fluxes • Si. O 2, Ti. O 2, Fe. O, Mg. O, Al 2 O 3 • Produces a gaseous shield to prevent contamination • Act as scavengers to reduce oxides • Add alloying elements to the weld • Influence shape of weld bead during solidification

Inert Gases • Argon, helium, nitrogen, and carbon dioxide • Form a protective envelope

Inert Gases • Argon, helium, nitrogen, and carbon dioxide • Form a protective envelope around the weld area • Used in • MIG • TIG • Shield Metal Arc

Vacuum • Produce high-quality welds • Used in electron beam welding • Nuclear/special metal

Vacuum • Produce high-quality welds • Used in electron beam welding • Nuclear/special metal applications • Zr, Hf, Ti • Reduces impurities by a factor of 20 versus other methods • Expensive and time-consuming

Types of Fusion Welding • • Oxyacetylene Cutting/Welding Shielded Metal Arc (“Stick”) Metal Inert

Types of Fusion Welding • • Oxyacetylene Cutting/Welding Shielded Metal Arc (“Stick”) Metal Inert Gas (MIG) Tungsten Inert Gas (TIG)

Oxyacetylene Welding • Flame formed by burning a mix of acetylene (C 2 H

Oxyacetylene Welding • Flame formed by burning a mix of acetylene (C 2 H 2) and oxygen TORCH TIP Inner Cone: 2700 -3500 deg C 1250 deg C Combustion Envelope 2100 deg C • Fusion of metal is achieved by passing the inner cone of the flame over the metal • Oxyacetylene can also be used for cutting metals

Shielded Metal Arc (Stick) • An electric arc is generated between a coated electrode

Shielded Metal Arc (Stick) • An electric arc is generated between a coated electrode and the parent metal • The coated electrode carries the electric current to form the arc, produces a gas to control the atmosphere and provides filler metal for the weld bead • Electric current may be AC or DC. If the current is DC, the polarity will affect the weld size and application

Shielded Metal Arc (con’t) • Process: • Intense heat at the arc melts the

Shielded Metal Arc (con’t) • Process: • Intense heat at the arc melts the tip of the electrode • Tiny drops of metal enter the arc stream and are deposited on the parent metal • As molten metal is deposited, a slag forms over the bead which serves as an insulation against air contaminants during cooling • After a weld ‘pass’ is allowed the cool, the oxide layer is removed by a chipping hammer and then cleaned with a wirebrush before the next pass.

Inert Gas Welding • For materials such as Al or Ti which quickly form

Inert Gas Welding • For materials such as Al or Ti which quickly form oxide layers, a method to place an inert atmosphere around the weld puddle had to be developed

Metal Inert Gas (MIG) • Uses a consumable electrode (filler wire made of the

Metal Inert Gas (MIG) • Uses a consumable electrode (filler wire made of the base metal) • Inert gas is typically Argon CONSUMABLE ELECTRODE DRIVE WHEELS POWER SOURCE SHIELDING GAS BASE METAL ARC COLUMN PUDDLE

Tungsten Inert Gas (MIG) • Tungsten electrode acts as a cathode • A plasma

Tungsten Inert Gas (MIG) • Tungsten electrode acts as a cathode • A plasma is produced between the tungsten cathode and the base metal which heats the base metal to its melting point • Filler metal can be added to the weld pool TUNGSTEN ELECTRODE POWER SOURCE TUNGSTEN ELECTRODE (CATHODE) ++ SHIELDING GAS BASE METAL ARC COLUMN PUDDLE ++ --BASE METAL (ANODE)

Welding Positions INCREASING DIFFICULTY FLAT HORIZONTAL VERTICAL OVERHEAD

Welding Positions INCREASING DIFFICULTY FLAT HORIZONTAL VERTICAL OVERHEAD

Weld Defects • Undercuts/Overlaps • Grain Growth • A wide T will exist between

Weld Defects • Undercuts/Overlaps • Grain Growth • A wide T will exist between base metal and HAZ. Preheating and cooling methods will affect the brittleness of the metal in this region • Blowholes • Are cavities caused by gas entrapment during the solidification of the weld puddle. Prevented by proper weld technique (even temperature and speed)

Weld Defects • Inclusions • Impurities or foreign substances which are forced into the

Weld Defects • Inclusions • Impurities or foreign substances which are forced into the weld puddle during the welding process. Has the same effect as a crack. Prevented by proper technique/cleanliness. • Segregation • Condition where some regions of the metal are enriched with an alloy ingredient and others aren’t. Can be prevented by proper heat treatment and cooling. • Porosity • The formation of tiny pinholes generated by atmospheric contamination. Prevented by keeping a protective shield over the molten weld puddle.

Residual Stresses • Rapid heating and cooling results in thermal stresses detrimental to joint

Residual Stresses • Rapid heating and cooling results in thermal stresses detrimental to joint strength. • Prevention • Edge Preparation/Alignment – beveled edges and space between components to allow movement • Control of heat input – skip or intermittent weld technique • Preheating – reduces expansion/contraction forces (alloys) and removes moisture from the surface • Peening – help metal stretch as it cools by hitting with a hammer. Use with care since it may work harden the metal • Heat Treatment – “soak” the metal at a high temperature to relieve stresses • Jigs and Fixtures – prevent distortion by holding metal fixed • Number of Passes – the fewer the better.

Joint Design BUTT JOINT FILLET JOINT STRAP JOINT LAP JOINT CORNER JOINT

Joint Design BUTT JOINT FILLET JOINT STRAP JOINT LAP JOINT CORNER JOINT

Generalized Welding Symbol FAR SIDE DETAILS Weld Geometry Electrode Material D L 1 -L

Generalized Welding Symbol FAR SIDE DETAILS Weld Geometry Electrode Material D L 1 -L 2 ARROW SIDE DETAILS Field weld symbol Weld all-around for pipes, etc. D = Weld Depth (usually equal to plate thickness) L 1 = Weld Length L 2 = Distance between centers for stitched welds The Field Weld Symbol is a guide for installation. Shipyards normally do not use it, except in modular construction.

Example Welding Symbol Geometry symbol for V-groove One-sided welds are max 80% efficient Two

Example Welding Symbol Geometry symbol for V-groove One-sided welds are max 80% efficient Two sided are 100% efficient 1/2 1/2”

Weld Symbols (Butt Joints) Backing

Weld Symbols (Butt Joints) Backing

Weld Symbol (Fillet Joints)

Weld Symbol (Fillet Joints)

Weld Symbol (Corner Joints)

Weld Symbol (Corner Joints)